To date, in a spark plug used for an internal combustion engine, a conductive seal layer is filled between a center electrode disposed at a front end side portion in a through hole of an insulator, and a member (for example, a resistor for removing noise) in the through hole on the side rearward of the center electrode. Thus, the center electrode is fixed in the insulator, and conductivity between the center electrode and the member on the side rearward thereof, and airtightness in the through hole are assured. For example, a conductive seal layer disclosed in Japanese Patent Application Laid-Open (kokai) No. 2010-135345 is formed by using conductive glass powder that contains Cu—Zn alloy powder the content of which is greater than 30% by mass and less than 75% by mass.